Generally, in an electrophotographic device such as a digital copying machine, a digital image signal, an image processing is carried out as follows, with respect to a digital image signal which is inputted from an input device such as a scanner. Namely, the digital image signal is outputted as an output image signal, after the digital image signal is: (I) subjected to digital-signal processing such as an input signal processing, a segmentation process, a color correction process, a black-generation process, and a zoom scaling process; and (II) further subjected to a filtration process using a spatial filter, and a halftone correction process.
FIG. 20 is a control block diagram illustrating the image processing of a conventional digital copying machine. The conventional digital copying machine includes: an input signal processing section 210; a segmentation process section 220; a color-correction/black-generation process section 230; a zoom scaling process section 240; a spatial filtration process section 250; a halftone correction process section 260; a pixel count section 270; and a toner consumption amount estimating section 280.
The following describes an image processing carried out in such a digital copying machine, with reference to FIG. 21.
First, an input digital-image signal of a document read in with a use of a scanner or the like is inputted to the input signal processing section 210, and is subjected to a pre-process for the subsequent image processing, and an image adjustment process such as an input-gamma correction and a conversion process (S201 and S202).
Next, the image signal is inputted to the segmentation process section 220, and a region-judgment is carried out for judging whether the image belongs to a character region, a halftone photographic region, or the like. Then, for each region thus judged, an identification signal (region identification signal) which indicates the type of each region is outputted(S203). The region identification signal is used in a subsequent process performed in the spatial filtration process section 250 or the halftone correction process section 260, in accordance with the type of region. For example, in the case of a halftone region, the region identification signal is used to carry out a smoothing-filtration process. In the case of the character region, the region identification signal is used to carry out an edge enhancement filtration process, or to change the halftone gamma characteristics to characteristics that shows a difference between a thick color and a light color more clearly.
A color-correction/black-generation process (Step: S204) to be carried out next, in the color-correction/black-generation process section 230, is a process which is necessitated in a case where the device is a color image forming apparatus. In the color-correction/black-generation process section 230, an RGB-image-signal having been transmitted from the segmentation process section 220 is converted into a CMYK (Cyan, Magenta, Yellow, Black)-image signal which is the final outputting format.
The image signal having converted into the CMYK-image signal is subjected to the zoom scaling process carried out in the zoom scaling process section 240 (S205), and then is inputted to the spatial filtration process section 250. In the spatial filtration process section 250, a suitable spatial filter is selected from a spatial filter table, in accordance with the region identification signal, a setting of an image mode, or the like. Then, by using the selected spatial filter, the spatial filtration process is carried out with respect to the CMYK-image-signal (S206). The spatial filter table is a table groups of filter coefficient, and is used as a reference at the time of the spatial filtration process. The table groups are selectively used in accordance with the circumstance.
Next, in the halftone correction process section 260, the halftone gamma property is corrected for a purpose of correcting a property of an output from an engine section (S207).
Further, the image signal subjected to the halftone correction process is inputted to a pixel count section 270, and then an accumulation process is carried out by using a counter while carrying out, on a pixel-to-pixel basis, a weighting process with respect to each signal of C, M, Y, and K (S208). After that, the output image signal is transmitted to an LSU, or an engine output-end of an LED (S210). In the toner consumption amount estimating section 280, a toner consumption amount is calculated for each color of C, M, Y, and K, based on an accumulated value obtained from the pixel count process (S209). The toner consumption amount thus calculated is for use in: a toner near-end judgment, accumulation of toner consumption amount data, or the like.
Further, on an engine-side of the digital copying machine, the following control is carried out, in order to restrain an aging-caused variation in, for example, a photoreceptor or a developer. Namely, a process condition is controlled, so as to achieve a constant toner density and/or a constant image output, since the first time operation of the copy machine until the end of its life. The process condition which is controlled is, for example, an exposure amount, an amount of toner density correction, and a developing bias value, or the like.
FIG. 22 is a flowchart providing a simple illustration of a toner density control process which is one of control processes carried out on the engine-side. In the toner density control process, a control value of a toner density sensor is determined based on a value of a life counter, a value of an environment sensor, or the like (S211, S212). An on/off operation of toner supply is controlled in accordance with this control value. In short, when the toner density is low (if resulting in “Yes” in S213), the toner supply is turned on so as to supply the toner (S214). Thus, a constant toner density is maintained.
Further, FIG. 23 is a flowchart providing a simple illustration of the halftone gamma correction process using a toner patch. In the halftone gamma correction process, a toner patch is formed, by using a halftone pattern (tones), on a photoreceptor or on a transfer belt (S221 to S223). This halftone pattern is obtained from a predetermined fixed input value. Then, an optical sensor or the like is used for reading an amount of light reflected from the toner patch (S224). Next, a sensor output value obtained from the read amount of reflection light is compared with a targeted value serving as a reference value, so as to calculate the correction amount (S225). In accordance with thus calculated correction amount, the current halftone gamma correction table is corrected (S226). This realizes a halftone gamma property which is always constant.
Next described in detail is how to calculate the toner consumption amount. Note that the following process is carried out on a color-by-color basis with respect to the colors of C, M, Y, and K (i.e., the process is carried out for each input signal of C, M, Y, and K).
The pixel count section 270 carries out, with respect to an input multi-valued image, the pixel count process as described below. As illustrated in FIG. 20, the pixel count section 270 includes: counting means 271; weighting calculation means 272; a weighting coefficient table 273; accumulating means 274.
The counting means 271 counts an input signal value of the inputted multi-value image (e.g. a multi tone image expressed in, for example, 16 tones or 256 tones) for each pixel. That is, the counting means 271 counts the input value (tone) of each pixel constituting the inputted multi-value image. For example, an input value which ranges from 0 to 15 is counted in the case of 16 tones.
The weighting calculation means 272 carries out the weighting process on the pixel-by-pixel basis, at the time the counting process is carried out by the counting means 271. More specifically, the weighting calculation means 272 acquires a weighting coefficient, corresponding to the input signal value of each pixel, from a weighting coefficient table 273, and multiplies the input signal value by the weighting coefficient so acquired. The weighting coefficient table 273 stores weighting coefficients respectively corresponding to input values of the pixels and used in the weighting process carried out by the weighting calculation means 272. As described, in the pixel count section 270, the pixel count process is carried out on the pixel-by-pixel basis, by using the counting means 271, the weighting calculation means 272, and the weighting coefficient table 273.
Then, the accumulating means 274 accumulates values of the respective pixels resulted from the pixel count process. More specifically, the weighting calculation means 272 multiplies the input signal value of each pixel by the weighting coefficient, and the accumulating means 274 accumulates the calculated values for all the pixels constituting the multi value image which has being inputted. Based on the accumulated value of the pixels calculated by the pixel count section 270, the toner consumption amount estimating section 280 estimates a toner consumption amount needed for the output image. The weighting coefficients stored in the weighting coefficient table 273 are values determined in advance. Table 1 below indicates an example of the weighting coefficient table 273, where the input signal value ranges from 0 to 15 in 16 values.
TABLE 1Weighting Coefficient (Fixed)INPUT SIGNALWEIGHTINGVALUECOEFFICIENTAREA 10-40AREA 25-81AREA 3 9-123AREA 413-154
In the case of Table 1, the input signal values are classified into 4 areas (area 1 to area 4) in accordance with the toner consumption amount. The weighting coefficient is determined for each of these areas. In the pixel-count process, the weighting process is carried out by selectively using, in accordance with the input signal values of 0 to 15, the weighting coefficients of the four areas.
FIG. 24 illustrates a relationship between the input signal values classified into the four areas of the weighting coefficient table of Table 1, and the weighting coefficients respectively associated with the input signal values. As illustrated in FIG. 24, a total area of the rectangles is substantially the same as an area below a curve indicating the toner consumption amount. Accordingly, it is possible to estimate the toner consumption amount from the total of the pixel-count values accumulated after the weighting process.
Japanese Unexamined Patent Publication No. 2002-287499 (Tokukai 2002-287499; published on Oct. 3, 2002) discloses an image forming apparatus which effectively prevents a variation in thin-toner layer, when continuously copying an image whose toner-consumption rate is extremely small. More specifically, the above publication discloses the image forming apparatus including: a pixel counter; a copy counter; and toner consuming means. This image forming apparatus forcedly executes a toner patch creating process when a less number of pixels than a predetermined value is counted, while a predetermined number of records are counted.
However, the conventional image forming apparatus such as a digital copying machine adopting the electro photographic system had the following problem.
Namely, as described above, when the toner consumption amount needed for the output image is calculated by carrying out the pixel-count process, storage means has been used as the weighting coefficient table, for storing the pre-fixed weighting coefficients. However, if such a weighting coefficient table is used, the weighting coefficient selected, from weighting coefficient table, for one input signal value may differ from a value on the curve indicating the toner consumption amount for the same input signal value, as illustrated in FIG. 24. Accordingly, the toner consumption amount may not be accurately calculated from the total value of the pixel values obtained from the weighting process.
In this case, for example, it is possible to reduce the difference between the actual toner consumption amount and the toner consumption amount estimated based on the pixel-count value, by using a weighting coefficient table, which stores the weighting coefficients respectively corresponding to each of the input signal values (i.e., each tone of the respective input signal), as illustrated in FIG. 25.
However, as indicated by a curve D (solid line) and a curve E (broken line) of FIG. 25, the toner consumption characteristic may vary amongst various models, or vary due to the aging or the like. Accordingly, by merely using the weighting coefficient table storing the weighting coefficients respectively corresponding to the tones of the input signal, it is not possible to follow the variation in the toner consumption characteristic amongst various models, or the variation in the toner consumption characteristic due to aging. As such, the difference between the actual toner consumption amount and the toner consumption amount estimated based on the pixel-count value cannot be reduced. This causes a problems that the toner consumption amount is not accurately estimated.